Oh wait, that was actually very very smart.
I forgot that i had in my rc file an older precompiled version from some experiments last night.
## >>> Root testing >>>
#source /opt/ROOT/prebuilt/root/bin/thisroot.sh
source /opt/ROOT/install/bin/thisroot.sh
cdir=$PWD
cd /opt/Geant4/install/bin
source geant4.sh
cd ${cdir}
## <<< Root testing <<<
This indeed will launch ROOT without an error!
/Library/Developer/CommandLineTools/SDKs % rc-update
/Library/Developer/CommandLineTools/SDKs % root
------------------------------------------------------------------
| Welcome to ROOT 6.32.06 https://root.cern |
| (c) 1995-2024, The ROOT Team; conception: R. Brun, F. Rademakers |
| Built for macosxarm64 on Oct 10 2024, 13:23:47 |
| From tags/6-32-06@6-32-06 |
| With Apple clang version 16.0.0 (clang-1600.0.26.3) |
| Try '.help'/'.?', '.demo', '.license', '.credits', '.quit'/'.q' |
------------------------------------------------------------------
root [0] .q
/Library/Developer/CommandLineTools/SDKs % rc-show